I think it entirely depends. Twitter and Facebook have deplatformed some people already (e.g. Milo Yiannopoulos) and I think given the history of their conduct,

I think it entirely depends. Twitter and Facebook have deplatformed some people already (e.g. Milo Yiannopoulos) and I think given the history of their conduct, that's fair. In the case of a whole party/movement, I would say it's a really fine line to walk. I wouldn't advocate for Facebook to ban parties like the AfD in Germany or FN in France, while they're often extremist, there is still some legitimate opposition within the bounds of the constitutions left in those parties. But I wouldn't be opposed to FB banning e.g. the KKK or some party that explicitly made reference to Mein Kampf or to killing all the Jews or similar. Also beware of the slippery slope fallacy. Just because one believes that deplatforming some parties or movements is legitimate, it doesn't mean nor necessarily lead to deplatforming all opposition.